1. Field of the Invention
The present invention relates to a semiconductor memory device containing an antifuse write voltage generation circuit, and more particularly to a semiconductor memory device in which the circuit scale of the antifuse write voltage generation circuit is reduced.
2. Description of the Related Art
In a large-capacity semiconductor memory, in particular DRAM, a redundant memory is provided to increase yield, and the columns or words where a defective bit is present are replaced with the redundant memory. Further, in semiconductor memories, a level of a high-potential internal power supply that is generated inside the memory is finely adjusted or the impedance of the output transistor is finely adjusted. The replacement with the redundant memory is performed by writing into a ROM the address information indicating which defective bit is to be replaced, and fine adjustment of the level or impedance is also performed by writing the fine adjustment information into the ROM.
A fuse ROM has been widely used for the ROM for writing the information at the final stage of the manufacturing process. For example, this is described in Japanese Patent Application Laid-open No. 07-287992, Japanese Patent Application Laid-open No. 2004-13930. In other words, the necessary information is written by irradiating a fuse element with a laser and blowing and cutting the fuse element.
Such fuse element ROM has the following limitations. Thus, a large-scale laser irradiation device is required and fuse melting can be performed only at the wafer stage.
Accordingly, an antifuse element ROM has recently been suggested to replace the fuse ROM. An antifuse has a configuration basically identical to a capacitor. In a non-writing state, the two terminals of the antifuse are open, and if writing is performed, the dielectric layer of the capacitor is short circuited and the two terminals are in a short circuit state. By using the antifuse, the surface area can be reduced comparing to that of the fuse, a large laser irradiation device becomes unnecessary, writing can be conducted by a high voltage generated internally, writing can therefore be conducted after the assembly process, and yield can be increased. A memory device using such antifuse is described, for example, in Japanese Patent Application Laid-open No. 11-328991.